Compression check

[gmarshall43]

What would be a good compression check for a 1971 Johnson, 9.5 hp, model number 9R-71R?????<br /><br />THANKS

 

[The Marine Doctor]

Re: Compression check

Anything above 100 psi a cyl..and close to even...for instance 110 110.<br /><br />TMD

 

[gmarshall43]

Re: Compression check

I get about 60 psi in each cylinder. That's a ways from 110 psi. What do you think the problem is and would this be the reason why it is hard to start???<br /><br />Radar

 

[Bradster941]

Re: Compression check

It actually starts?<br /><br />Sorry, but at 60 psi it's way past time for rebuild.

 

[The Marine Doctor]

Re: Compression check

Yes...it would definately be hard starting. The air/fuel is not being compressed to the point of being able to be ignited by the sparkplug.<br /><br />TMD

 

[ezeke]

Re: Compression check

Hate to disagree with all this talent, but I own 6 of these omc 9.5 models, 1967-1973, and keep them all running. They were always loose and I rarely get very high compression unless the motor is warm from running and well lubricated. <br />Before you dump the motor, take it out and run it.<br />If it works, don't fix it. The main concern is that the compression is balanced between the cylinders. <br />These motors always fouled plugs so I use Champion J6J, 89 or higher octane and a blended synthetic oil. No problems this season.

 

[gmarshall43]

Re: Compression check

Thanks for all the responses even though they conflict a bit. I bought a Seloc service manual and it didn't give a compression rating but was more concern about having the compression in the two cyclinders even which they are. Are these manuals reliable?